This invention relates generally to metal alloys and more particularly to a method of atomizing metal to produce a powder and to a powder produced thereby.
Metal powders are useful in producing shaped metal pieces formed by explosive consolidation for example. One such metal powder is Type 304 stainless steel. A known method for producing metal powder is centrifugal atomization. Metal is forced from a melt to the surface of a rotating cup. Droplets of metal flung from the surface of the cup form atomized metal powder. Quench gas is used to quench the airborne metal powder. The powder can then be collected by such means as a cyclone separator. The atmospheres in which the melt is maintained and in which the powder is quenched will affect characteristics of the metal powder produced. One characteristic is its fineness. Another is the amount of gas entrained therein. Other methods exist for entraining gas in metal.
Utilization of helium, an inert gas, in the melt atmosphere or in the quench gas is known in prior art methods. Helium is known as a quench gas. P.R. Holiday, A.R. Cox, and R.J. Patterson II, "Rapid Solidification Effects on Alloy Structures," Proc. Int'l Conf. on Rapid Solidification Processing, Nov. 13-16, 1977, (Claitor's Publishing Division, Baton Rouge, La, 1978). As illustrated in U.S. Pat. No. 4,610,719, it can also be used to pressurize a melt in a process for enhancing fineness of powder. While some degree of entrainment of helium in metal may be inherent in such processes, it is not generally regarded as desirable. H. Ullmaier, "The Influence of Helium on the Bulk Properties of Fusion Reactor Structural Materials," Nuclear Fusion, 24, (1984), pp. 1029-1083, discusses helium embrittlement of Type 304 stainless steel.
In accordance with the present invention, however, helium, and/or other gas, is combined in a predetermined manner to provide metals with improved properties by new methods.